rub salt into one's wounds
A:You shouldn't have criticized your son in front of his friends.
A:你不应该当着你儿子朋友的面批评他。B:Why? He did something wrong.
B:为什么?他做错事了。
A:I know. But at that time your blame is rubbing salt into his wounds.
A:我知道，但当时你的批评是火上浇油。B:I only wanted to help him.
B:我只是想帮他。A:But it's not the right time.
A:但时机不对。